Optogenetics is a promising new technique in neuroscience, combining optical and genetic techniques to probe neural circuits. It relies on microbial opsins, light sensitive proteins, to manipulate the activity of neurons in response to flashes of light. New genetic techniques developed in parallel allow neuroscientists the ability to select specific types of neurons for optogenetic control. By perturbing the activity of specific neurons in live animals, neuroscientists can determine the role that the neurons play in the expression of behavior. In addition, optogenetic techniques developed to study the brain in the lab may be useful in treating a wide range of neurological disorders in the clinic. In order to move optogenetics from the proof-of-principle stage to routine use in the lab and the clinic, a set of optimized techniques and equipment need to be developed.
In order to optically stimulate the brain of freely moving animals, drug delivery cannula systems have been re-purposed to allow an optical fiber to pass through a guide cannula that is implanted through the skull of the animal. The guide cannula is typically connected to a pedestal, which is mounted on the head of the animal using a screw interface, cranioplastic cement, dental cement and/or other bonding materials. Threading or clips may be used to attach the guide cannula to an external device. The screw type connection used to hold the fiber in place in these systems does not allow for free rotation and can be difficult to connect to un-anaesthetized animals. Optical fibers are more fragile than the fluid delivery cannula these systems were designed for and as a result, fiber breakage is a common problem. In addition, the guide cannula is open to the brain, allowing the entry of blood and fluid into the cannula and bacterial contamination into the brain from external sources. With chronic stimulation, repeated insertion and withdrawal of the fiber and dummy plug can damage the brain structure under study.
In addition, neurophysiologists have used acute single electrode recordings in anesthetized animals to study neurons in the brain. More recently, chronic multi-electrode recordings in awake, behaving animals have been used due, in part, to the realization that many neural systems behave very differently in the anesthetized brain. Neuro-engineers first hand-built electrode assemblies, and as the technique gained acceptance, several companies (such as Plexon, Inc., Dallas, Tex., U.S.A.) have commercialized multi-electrode assemblies and equipment. A significant enhancement in the quality of chronic recordings came with the invention of headstage amplifiers. These tiny printed circuits may be situated directly on the head of the animal to boost and condition neural signals prior to sending them through a cable to the main amplifiers. Headstage amplifiers may be used to interface high impedance electrodes with low impedance cables and also to boost gain. Thus, headstages are now standard equipment for chronic recording experiments. However, the connectors that are typically used to connect the headstage to the implanted electrodes may be highly susceptible to the stresses of head movement in an awake animal despite being small and lightweight. Thus, when the connector flexes, the electrical contacts may move and generate noise which overwhelms the neural signal. For studying behavioral tasks that may involve movement, the noise may be a significant problem to obtaining useful data.